Transformers permanently connected to power lines for the purpose of powering doorbells, home heating and cooling controls, and the like, dissipate a significant amount of energy during intervals when these transformers are not delivering power to their intermittently-connected loads. This invention substantially reduces current flow during intervals when the secondary winding of such an energized transformer is not connected to an electrical load.
A first object of this invention is to interrupt the flow of current to the primary side of the transformer when the transformer secondary is disconnected from the load.
A second object of this invention is to sense, with circuitry connected only on the primary side of said transformer, the presence of a load on the secondary side.
A third object of this invention is to connect the transformer primary to the power source when a load on the secondary has been sensed.
A fourth object of this invention is to achieve the above-listed objectives with a two-terminal circuit to minimize the cost of installing this invention in electrical systems.
A fifth object of this invention is to achieve the above-listed objectives with no reduction in isolation between primary and secondary sides of the transformer.
A sixth object of this invention is to achieve the above-listed objectives with a circuit configuration that will facilitate the inclusion of most elements of the invention within an inexpensive monolithic microcircuit.